A new type of hydrogen-bonding interaction in the diborane (B2H6)center dot center dot center dot pi (benzene C6H6, 1,3-cyclopentadiene C5H6, and cyclobutadiene C4H4) system is identified with the natural bond orbital and atoms-in-molecules analyses based on ab initio calculations. In comparison with the symmetric and asymmetric stretching vibrational modes of the bridging hydrogen atoms in free B2H6, the frequencies of the symmetric mode are red-shifted for B2H6 center dot center dot center dot C6H6 and B2H6 center dot center dot center dot C5H6 but blue-shifted for B2H6 center dot center dot center dot C4H4. The frequency blue shifts of the asymmetric mode are found for all three complexes; the most significant blue shift is 14.73 cm(-1) for the asymmetric mode in B2H6 center dot center dot center dot C4H4. In these complexes, the electron-deficient three-center two-electron bond B-H-1-B facing the pi orbital is shortened, while the opposite B-H-2-B bond is elongated.